Dan Legard, Chang-Lin Xiao, and James Mertely
INTRODUCTION
The following report is a summary of the fungicide evaluation trials for Botrytis fruit rot, powdery mildew, and anthracnose fruit rot conducted at GCREC-Dover during the 1998 to 1999 season. These reports contain results for experimental and unlabeled fungicides along with products currently labeled for use on strawberry. These results are intended to provide growers and industry representatives with an overview of the effectiveness of new fungicides currently being evaluated for strawberry in Florida. Results from these studies are used by agrochemical companies, the University of Florida, and the FSGA to identify fungicides for further study and ultimately their labeling for use on strawberry in Florida.
EVALUATION OF FUNGICIDES TO CONTROL BOTRYTIS FRUIT ROT OF STRAWBERRY DURING THE
1998 TO 1999 SEASON.
Bare root plants of cultivar Sweet Charlie from Canada were transplanted into plastic-mulched raised beds on 4 ft centers (28 inches wide and 7 inches high at the center and 6 inches high at the edge), in methyl bromide: chloropicrin (98:2) fumigated soil on 15 Oct, 1998. Plants were spaced 11 inches apart within row and 12 inches apart between rows, and overhead irrigated for 10 days to establish the transplants, then irrigated and fertilized by drip tape. Fungicide treatments were applied with a CO2 backpack sprayer (100 GPA).
Treatments were applied weekly beginning on 4 November 1998 except where noted. Bloom sprays were timed to provide coverage during the first two peak bloom periods. Fungicides were applied to the first bloom beginning on 18 November, and on the second bloom beginning on 23 December. For most treatments two bloom sprays were applied during each bloom period for a total of 4 applications. In the three treatments with bloom sprays of both Elevate and Rovral, four applications were applied during each bloom period 7 days apart. The experiment consisted of a randomized complete block design with four replicates, each with 16 plants in two rows per bed, 8 plants per row. Fruit were harvested twice a week from 7 December 98 through 9 March 99 but only one harvest each week was graded and used to determine Botrytis fruit rot incidence and marketable yield (15 harvests). Numbers reported are percent of fruit harvested with Botrytis (B. cinerea) fruit rot (number of berries with Botrytis divided by total number of marketable and unmarketable fruit harvested), and total marketable yield (grams / plot were converted to flats per acre and doubled to best estimate potential yields). Botrytis incidence data were transformed (arc sine square root) before statistical analysis. A two way ANOVA was conducted and means were separated by Fisher’s protected LSD (P£ 0.05).
Weather during the 1998 to 1999 season was warmer and drier than normal. The higher average temperatures during the season produced faster plant growth. The increased plant growth and warm temperatures resulted in an early second peak bloom that did not produce much fruit. The experiment was continued until fruit from the third peak bloom was harvested. A severe Botrytis fruit rot epidemic developed and significant treatment differences (P£0.05) in marketable yield and Botrytis fruit rot incidence were found (Table 1). The most effective treatments included weekly applications of Thiram or Captan with bloom sprays of Elevate, Switch and/or Rovral. Thiram 4L provided excellent control of Botrytis at the 1 gal and 2 gal rates.
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EVALUATION OF FUNGICIDES TO CONTROL POWDERY MILDEW OF STRAWBERRY, 1998 TO 1999
SEASON.
Bare root plants of ‘Camarosa’ from Canada were transplanted 15 October, 1998. Plants were spaced 15 inches apart within row and 12 inches apart between rows, and overhead irrigated for 10 days to establish the transplants, then irrigated and fertilized by drip tape. Fungicide treatments were applied with a CO2 backpack sprayer (100 GPA). Treatments were applied in 100 gallons/acre either weekly or every two weeks from 24 October 97 through 25 March 98 (23 weeks) as noted in the table. Captan (3 lb active ingredient (a.i.) /acre) was applied weekly by tractor (100 GPA) to the entire experiment for the last 6 weeks of the season to control Botrytis fruit rot. The experiment consisted of a randomized complete block design (four replicates) with 14 plants in two rows per bed, 7 plants per row. Fruit were harvested twice weekly from 7 December 98 to 19 March 99 (30 harvests) and marketable yield determine. The number of unmarketable, powdery mildew infected, and Botrytis infected (gray mold) fruit were also determined. Numbers reported are percent of fruit harvested with powdery mildew (Sphaerotheca macularis) (number of fruit with noticeable powdery mildew mycelium on it, divided by total number of marketable and unmarketable fruit harvested), and total marketable yield reported (flats per acre @ 10.25 lbs per flat). Foliar disease severity was rated once during the season (21 Jan 99). Individual plots were visually rated for disease severity on a 0-5 scale (0: no disease, 1: less than 10% of foliage affected, 2: 10-25% affected, 3: 25-50% affected, 4: 50-75% affected, 5: greater than 75% affected). Powdery mildew fruit damage data was transformed (arc sine square root) prior to analysis. Data were evaluated by two way ANOVA and significant treatment effects were found for marketable yield, incidence of powdery mildew on fruit and foliar severity. Botrytis fruit rot incidence is also reported because the epidemic was severe and significant treatment differences were observed. Treatment means were separated by Fisher’s protected LSD (P £ 0.05).
Weather during the 1998-1999 strawberry season was extremely warm and dry. A severe powdery mildew and gray mold epidemic developed within the experiment. Significant differences were observed between treatments in the control of powdery mildew (Table 2). The incidence of fruit damaged by powdery mildew was lowest with the weekly sulfur applications; however, these treatments also had significantly more Botrytis fruit rot. The high rate of Nova (5.0 oz) provided the best foliar control of powdery mildew when ratings were made in January during the severest part of the epidemic.